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[[Kategori:Periode dalam tabel periodik]]
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{{Periodic table (micro)| title=Period 1 in the [[periodic table]] | mark=H,He}}
A '''period 1 element''' is one of the [[chemical element]]s in the first row (or [[Periodic table period|period]]) of the [[periodic table|periodic table of the chemical elements]]. The periodic table is laid out in rows to illustrate recurring (periodic) trends in the chemical behaviour of the elements as their atomic number increases: a new row is begun when chemical behaviour begins to repeat, meaning that elements with similar behaviour fall into the same vertical columns. The first period contains fewer elements than any other row in the table, with only two: [[hydrogen]] and [[helium]]. This situation can be explained by modern theories of [[atomic structure]]. In a [[quantum mechanics|quantum mechanical]] description of [[atom]]ic structure, this period corresponds to the filling of the [[s-block|1s]] [[atomic orbital|orbital]]. Period 1 elements obey the [[octet rule#Exceptions|duet rule]] in that they need two [[electron]]s to complete their [[valence shell]]. The maximum number of electrons that these elements can accommodate is two, both in the 1s orbital. Therefore, period 1 can have only two elements.
==Periodic trends==
{{double image|right|Electron shell 001 Hydrogen (diatomic nonmetal) - no label.svg|100|Electron shell 002 Helium - no label.svg|100|[[Hydrogen]]|[[Helium]]|Hydrogen's electron configuration is 1.|Helium's electron configuration is 2.}}
All other periods in the period table contain at least 8 elements, and it is often helpful to consider [[periodic trends]] across the period. However, period 1 contains only two elements, so this concept does not apply here.
In terms of vertical trends down groups, helium can be seen as a typical [[noble gas]] at the head of [[Group 18]], but as discussed below, hydrogren's chemistry is unique and it is not easily assigned to any group.
==Position of period 1 elements in the periodic table==
Although both hydrogen and helium are in the [[s-block]], neither of them behaves similarly to other s-block elements. Their behaviour is so different from the other s-block elements that there is considerable disagreement over where these two elements should be placed in the periodic table.
[[Hydrogen]] is sometimes placed above [[lithium]],<ref name="iupac" /> above [[carbon]],<ref name="hydrogen">{{cite journal |last=Cronyn |first=Marshall W. |title=The Proper Place for Hydrogen in the Periodic Table |journal=Journal of Chemical Education |volume=80 |issue=8 |date=August 2003 |pages=947–951 |doi=10.1021/ed080p947 |bibcode=2003JChEd..80..947C}}</ref> above [[fluorine]],<ref name="hydrogen" /><ref name="hydrogen-halogen">{{cite web |url=http://hydrogentwo.com/hydrogen-halogen.html |title=Hydrogen is a Halogen |author=Vinson, Greg |year=2008 |work=HydrogenTwo.com |publisher= |accessdate=January 14, 2012}}</ref> above both lithium and fluorine (appearing twice),<ref name="chemistry-international" /> or left floating above the other elements and not assigned to any group<ref name="chemistry-international">{{cite journal |last1=Kaesz |first1=Herb |last2=Atkins |first2=Peter |date=November–December 2003 |title=A Central Position for Hydrogen in the Periodic Table |journal=Chemistry International |volume=25 |issue=6 |pages=14 |publisher=[[International Union of Pure and Applied Chemistry]] |url=http://www.iupac.org/publications/ci/2003/2506/ud.html |accessdate=January 19, 2012}}</ref> in the [[periodic table]].
[[Helium]] is almost always placed above [[neon]] (which is in the [[p-block]]) in the periodic table as a [[noble gas]],<ref name="iupac">{{cite web|url=http://old.iupac.org/reports/periodic_table/ |title=International Union of Pure and Applied Chemistry > Periodic Table of the Elements |publisher=IUPAC |accessdate=2011-05-01}}</ref> although it is occasionally placed above [[beryllium]] due to their similar electron configuration.<ref name="janet-table">{{cite web |url=http://www.webelements.com/nexus/Janet_Periodic_Table |title=Janet periodic table |author=Winter, Mark |date=1993–2011 |work=WebElements |accessdate=January 19, 2012}}</ref>
{{clear}}
==Elements==
{| class="wikitable"
|-
! colspan="3" | [[Chemical element]] !! [[Chemical series]] !! [[Electron configuration]]
|- style="background-color: {{element color|diatomic nonmetal}}"
| 1 || '''H''' || [[Hydrogen]] || [[Diatomic nonmetal]] || 1s<sup>1</sup>
|- style="background-color: #c0ffff"
| 2 || '''He''' || [[Helium]] || [[Noble gas]] || 1s<sup>2</sup>
|}
===Hydrogen===
{{Main|Hydrogen}}
[[File:Hydrogen discharge tube.jpg|thumb|left|150px|Hydrogen discharge tube]]
[[File:Deuterium discharge tube.jpg|thumb|left|150px|Deuterium discharge tube]]
Hydrogen (H) is the [[chemical element]] with [[atomic number]] 1. At [[standard temperature and pressure]], hydrogen is a colorless, odorless, [[nonmetal]]lic, tasteless, highly [[combustion|flammable]] [[Diatomic molecule|diatomic]] [[gas]] with the [[molecular formula]] H<sub>2</sub>. With an [[atomic mass]] of 1.00794 amu, hydrogen is the lightest element.<ref>{{cite web|accessdate=2008-07-15|url=http://www.eia.doe.gov/kids/energyfacts/sources/IntermediateHydrogen.html|title=Hydrogen – Energy |publisher=Energy Information Administration}}</ref>
Hydrogen is the most [[abundance of the chemical elements|abundant]] of the chemical elements, constituting roughly 75% of the universe's elemental mass.<ref>{{cite web | last=Palmer | first=David | date=November 13, 1997 | url=http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/971113i.html | title=Hydrogen in the Universe | publisher=NASA | accessdate=2008-02-05}}</ref> [[Star]]s in the [[main sequence]] are mainly composed of hydrogen in its [[plasma (physics)|plasma]] state. Elemental hydrogen is relatively rare on [[Earth]], and is industrially produced from [[hydrocarbon]]s such as methane, after which most elemental hydrogen is used "captively" (meaning locally at the production site), with the largest markets almost equally divided between [[fossil fuel]] upgrading, such as [[hydrocracking]], and [[ammonia]] production, mostly for the fertilizer market. Hydrogen may be produced from water using the process of [[electrolysis]], but this process is significantly more expensive commercially than hydrogen production from natural gas.<ref>{{cite web | author=Staff | year=2007 | url=http://www.fsec.ucf.edu/en/consumer/hydrogen/basics/production.htm | title=Hydrogen Basics — Production | publisher=Florida Solar Energy Center | accessdate=2008-02-05}}</ref>
The most common naturally occurring [[isotope]] of hydrogen, known as [[hydrogen-1|protium]], has a single [[proton]] and no [[neutron]]s.<ref>{{cite news|title=Fusion Power Is Still Facing Formidable Difficulties|work=The New York Times|date=1971-03-11|author=Sullivan, Walter}}</ref> In [[ionic compound]]s, it can take on either a positive charge, becoming a [[Ion|cation]] composed of a bare proton, or a negative charge, becoming an [[Ion|anion]] known as a [[hydride]]. Hydrogen can form compounds with most elements and is present in [[water]] and most [[organic compound]]s.<ref>{{cite encyclopedia|encyclopedia=[[Encyclopædia Britannica]]|year=2008|title=hydrogen}}</ref> It plays a particularly important role in [[acid-base reaction theories|acid-base chemistry]], in which many reactions involve the exchange of protons between soluble molecules.<ref>{{cite journal|title=Electron-Driven Acid-Base Chemistry: Proton Transfer from Hydrogen Chloride to Ammonia|date=2008-02-15|volume=319|issue=5865|pages=936–939|doi=10.1126/science.1151614|author=Eustis, S. N.|journal=Science|pmid=18276886|last2=Radisic|first2=D|last3=Bowen|first3=KH|last4=Bachorz|first4=RA|last5=Haranczyk|first5=M|last6=Schenter|first6=GK|last7=Gutowski|first7=M|bibcode = 2008Sci...319..936E }}</ref> As the only neutral atom for which the [[Schrödinger equation]] can be solved analytically, study of the energetics and [[atomic spectrum|spectrum]] of the hydrogen atom has played a key role in the development of [[quantum mechanics]].<ref>{{cite encyclopedia|encyclopedia=[[Encyclopædia Britannica]]|year=2008|title= Time-dependent Schrödinger equation}}</ref>
The interactions of hydrogen with various metals are very important in [[metallurgy]], as many metals can suffer [[hydrogen embrittlement]],<ref>{{cite journal | last=Rogers | first=H. C. | title=Hydrogen Embrittlement of Metals | journal=Science | year=1999 | volume=159 | issue=3819 | pages=1057–1064 | doi=10.1126/science.159.3819.1057 | pmid=17775040|bibcode = 1968Sci...159.1057R }}</ref> and in developing safe ways to store it for use as a fuel.<ref>{{cite news | last=Christensen | first=C. H. |author2=Nørskov, J. K. |author3=Johannessen, T. | date=July 9, 2005 | title=Making society independent of fossil fuels — Danish researchers reveal new technology | publisher=Technical University of Denmark | url=http://www.dtu.dk/English/About_DTU/News.aspx?guid=%7BE6FF7D39-1EDD-41A4-BC9A-20455C2CF1A7%7D | accessdate=2008-03-28}}</ref> Hydrogen is highly soluble in many compounds composed of [[Rare earth element|rare earth metals]] and [[transition metal]]s<ref name="Takeshita">{{cite journal | last=Takeshita | first=T. |author2=Wallace, W.E. |author3=Craig, R.S. | title=Hydrogen solubility in 1:5 compounds between yttrium or thorium and nickel or cobalt | journal=Inorganic Chemistry | year=1974 | volume=13 | issue=9 | pages=2282–2283 | doi = 10.1021/ic50139a050}}</ref> and can be dissolved in both [[crystalline]] and [[amorphous solid|amorphous]] metals.<ref name="Kirchheim1">{{cite journal | last=Kirchheim | first=R. |author2=Mutschele, T. |author3=Kieninger, W | title=Hydrogen in amorphous and nanocrystalline metals | journal=Materials Science and Engineering | year=1988 | volume=99 | pages=457–462 | doi = 10.1016/0025-5416(88)90377-1}}</ref> Hydrogen solubility in metals is influenced by local distortions or impurities in the metal [[crystal lattice]].<ref name="Kirchheim2">{{cite journal | last=Kirchheim | first=R. | title=Hydrogen solubility and diffusivity in defective and amorphous metals | journal=Progress in Materials Science | year=1988 | volume=32 | issue=4 | pages=262–325 | doi = 10.1016/0079-6425(88)90010-2}}</ref>
===Helium===
{{Main|Helium}}
[[File:Helium discharge tube.jpg|left|thumb|upright|150px|Helium discharge tube]]
Helium (He) is a colorless, odorless, tasteless, non-toxic, [[inert]] [[monatomic]] chemical element that heads the [[noble gas]] series in the [[periodic table]] and whose [[atomic number]] is 2.<ref>{{cite web|accessdate=2008-07-15|url=http://www.webelements.com/helium/|title=Helium: the essentials |publisher=WebElements}}</ref> Its [[boiling point|boiling]] and [[melting point|melting]] points are the lowest among the elements and it exists only as a [[gas]] except in extreme conditions.<ref>{{cite web|accessdate=2008-07-15|url=http://www.webelements.com/helium/physics.html|title=Helium: physical properties |publisher=WebElements}}</ref>
Helium was discovered in 1868 by French astronomer [[Pierre Janssen]], who [[discovery of the chemical elements|first detected]] the substance as an unknown yellow [[spectroscopy|spectral line]] signature in light from a [[solar eclipse]].<ref>{{cite web|accessdate=2008-07-15|url=http://encarta.msn.com/encyclopedia_762508746/pierre_janssen.html|title=Pierre Janssen |publisher=MSN Encarta}}</ref> In 1903, large reserves of helium were found in the [[natural gas field]]s of the United States, which is by far the largest supplier of the gas.<ref>{{cite web|accessdate=2008-07-15|url=http://www.blm.gov/wo/st/en/info/newsroom/2007/january/NR0701_2.html|title=Where Has All the Helium Gone? |publisher=Bureau of Land Management|date=2007-01-18|author=Theiss, Leslie}}</ref> The substance is used in [[cryogenics]],<ref>{{cite book|title=Cryogenic Engineering: Fifty Years of Progress|author=Timmerhaus, Klaus D.|date=2006-10-06|publisher=Springer|isbn=0-387-33324-X}}</ref> in deep-sea breathing systems,<ref>{{cite journal|title=Helium voice unscrambling|author=Copel, M.|journal=Audio and Electroacoustics|volume=14|issue=3|date=September 1966|pages=122–126|doi=10.1109/TAU.1966.1161862}}</ref> to cool [[superconducting magnet]]s, in [[helium dating]],<ref>{{cite encyclopedia|encyclopedia=[[Encyclopædia Britannica]]|year=2008|title=helium dating}}</ref> for inflating [[balloon]]s,<ref>{{cite web|accessdate=2008-07-15|url=http://www.howstuffworks.com/helium.htm|title=How Helium Balloons Work |publisher=How Stuff Works|author=Brain, Marshall}}</ref> for providing lift in [[airship]]s,<ref>{{cite web|accessdate=2008-07-15|url=http://www.popsci.com/military-aviation-space/article/2008-07/return-blimp|title= The Return of the Blimp |work=Popular Science|date=2008-07-10|author=Jiwatram, Jaya}}</ref> and as a protective gas for industrial uses such as [[arc welding]] and growing [[silicon]] wafers.<ref>{{cite journal|title=When good GTAW arcs drift; drafty conditions are bad for welders and their GTAW arcs.|journal=Welding Design & Fabrication|date=2005-02-01}}</ref> Inhaling a small [[volume]] of the gas temporarily changes the timbre and quality of the human voice.<ref>{{cite web|accessdate=2008-07-15|url=http://www.sciam.com/article.cfm?id=why-does-inhaling-helium|title=Why does inhaling helium make one's voice sound strange? |work=Scientific American|date=2006-09-04|author=Montgomery, Craig}}</ref> The behavior of liquid helium-4's two fluid phases, helium I and helium II, is important to researchers studying [[quantum mechanics]] and the phenomenon of [[superfluidity]] in particular,<ref>{{cite web|accessdate=2008-07-15|url=http://www.sciencedaily.com/releases/2004/09/040903085531.htm|title=Probable Discovery Of A New, Supersolid, Phase Of Matter |publisher=Science Daily|date=2004-09-03}}</ref> and to those looking at the effects that temperatures near [[absolute zero]] have on [[matter]], such as with [[superconductivity]].<ref>{{cite news|title=Scientists See Peril In Wasting Helium; Scientists See Peril in Waste of Helium|work=The New York Times|date=1979-08-21|author= Browne, Malcolm W.}}</ref>
Helium is the second lightest element and is the second most [[chemical abundance|abundant]] in the observable universe.<ref>{{cite web|accessdate=2008-07-15|url=http://www.webelements.com/helium/geology.html|title=Helium: geological information |publisher=WebElements}}</ref> Most helium was formed during the [[Big Bang]], but new helium is being created as a result of the [[nuclear fusion]] of hydrogen in [[star]]s.<ref>{{cite web|accessdate=2008-07-15|url=http://www.newscientist.com/article/mg12517027.000-origin-of-the-chemical-elements.html|title=Origin of the chemical elements
|work=New Scientist|date=1990-02-03|author=Cox, Tony}}</ref> On [[Earth]], helium is relatively rare and is created by the natural [[radioactive decay|decay]] of some radioactive elements<ref>{{cite news|title=Helium supply deflated: production shortages mean some industries and partygoers must squeak by.|publisher=Houston Chronicle|date=2006-11-05}}</ref> because the [[alpha particle]]s that are emitted consist of helium [[atomic nucleus|nuclei]]. This radiogenic helium is trapped with [[natural gas]] in concentrations of up to seven percent by volume,<ref>{{cite web|accessdate=2008-07-15|url=http://www.aapg.org/explorer/2008/02feb/helium.cfm|title=Helium a New Target in New Mexico |publisher=American Association of Petroleum Geologists|date=2008-02-02|author=Brown, David}}</ref> from which it is extracted commercially by a low-temperature separation process called [[fractional distillation]].<ref>{{cite news|title=Where Do We Get the Helium We Use?|publisher=The Science Teacher|date=2006-12-01|author=Voth, Greg}}</ref>
==References==
{{Reflist|2}}
==Further reading==
{{Wikipedia books|Period 1 elements}}
* {{cite book
|author=Bloch, D. R.
|year=2006
|title=Organic Chemistry Demystified
|url=http://books.google.com/?id=yVPcSIn5xjAC
|publisher=McGraw-Hill Professional
|isbn=0-07-145920-0
|ref=CITEREFBloch2006
}}
{{Compact periodic table}}
{{Navbox periodic table}}
{{good article}}
{{DEFAULTSORT:Period 01}}
[[Category:Periods in the periodic table]]
[[Category:Pages containing element color directly]]
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